1) Field of the Invention
The present invention relates to an electric motor drive apparatus for driving an electric motor and a motor-driven power steering system for the assistance in control force for steering (steering wheel).
2) Description of the Related Art
In a conventional motor-driven power steering system equipped with an electric motor drive apparatus for the assistance in control force for steering, when the temperature of an output stage for driving an electric motor exceeds a critical value, the upper limit value of current flowing in the output stage is decreased to prevent a large current from flowing in the electric motor (for example, see Japanese Patent Laid-Open No. 2000-255443).
However, for example, even in a case in which the current flowing in the output stage rapidly varies largely from a low condition, since the temperature of the output stage does not rise immediately, in the case of the aforesaid motor-driven power steering system in which the upper limit value of current flowing in the electric motor is decreased after the temperature of the output stage exceeds the critical value, there is a problem in that a large current continuously flows in the electric motor from when the temperature of the output stage starts to rise until it exceeds the critical value, which exerts adverse effects thereon.